The Internet comprises a vast number of computers and computer networks that are interconnected through communication links, with information being exchanged using various services such as electronic mail and the World Wide Web (also referred to as the “Web”). In addition to providing access to information, the Web has become a medium that is used to search for, shop for and order items (such as products, services and/or information) that are for purchase, rent, lease, license, trade, evaluation, sampling, subscription to, etc. In many circumstances, a user can visit the Web site of a Web merchant (or a “Web store”) or otherwise interact with an online retailer or electronic marketplace that provides one or more items, such as to view information about the items, give an instruction to place an order for one or more items, and provide information needed to complete the purchase (e.g., payment and shipping information). The Web merchant then fulfills the order by providing the ordered items to the indicated recipient, such as by providing product items that have been ordered through physical distribution channels (e.g., shipment via a governmental postal service or private common carrier) or electronically (e.g., via download over the Internet, such as for digital music or videos) as appropriate. Ordered service items may similarly be provided electronically (e.g., providing email service) or physically (e.g., performing cleaning services at the purchaser's house).
The widespread popularity of the Web has also provided additional opportunities for computers to inter-communicate in various programmatic manners. For example, there is growing use of the Web to provide so-called “Web services,” which typically involve the programmatic interaction of remote applications to exchange information via defined APIs (“application program interfaces”), or the like. Web services may allow heterogeneous applications and computers to interact, and can be defined and implemented using a variety of underlying protocols and techniques. For example, some Web service implementations return data in XML (“eXtensible Markup Language”) format using HTTP (“HyperText Transport Protocol”) in response to a Web service invocation request specified as a URI (“Uniform Resource Identifier”), such as a URL (“Uniform Resource Locator”) that includes a specified operation and one or more query parameters. In other implementations, additional underlying protocols are used for various purposes, such as SOAP (“Simple Object Access Protocol”) for standard message exchange, WSDL (“Web Services Description Language”) for description of service invocations, and UDDI (“Universal Description, Discovery, and Integration service”) for discovery of available services.